an international system for arranging books in a library Culture The Dewey system was invented by Melvil Dewey (1851-1931), a US librarian. Dewey gave every subject a number between 0 and 999. Every book in a library is given one of these numbers so that books on a particular subject are easy to find. New subjects have been added to Dewey's original list by using decimal numbers, e.g. 331.1, 331.2, etc. Word Origin late 19th cent.: named after Melvil Dewey (1851–1931), American librarian.